You have to actually try to build a gem so this is easy!
to use bundler without Rails, a gem, whatever just create a directory
mkdir my-non-gem-project
cd my-non-gem-project
install bundler
gem install bundler
and initialize your Gemfile
bundle init
that will create a Gemfile
for you and you can add to it and run bundle
to install the dependencies from it
The simplest way to use bundler in your project would then be to open your main app file and add
require 'bundler/setup'
Bundler.require
This will require all of the gems you have in your Gemfile in the file this is added to. I am pretty sure that this file must be in the same directory as your Gemfile. More information here
Have fun with your Ruby project!